Challenge-response

Challenge-response protocol is used frequently in password authentication. The challenge is presented when an administrator requests a password - the response occurs when another party provides an appropriate answer to become authenticated. The downside of challenge-response protocol is that an outside party can eavesdrop on the password authentication process to authenticate itself in the same way. One solution that has been used to combat this vulnerability is the issuing of multiple passwords, each one marked with it’s own identifier. An administrator can choose from a number of identifiers and require a user to provide the correct password pertaining to that identifier. When an intruder intercepts a pair of challenge-response messages, their chance of responding correctly to the combined challenge are drastically reduced. Challenge-response protocol is also used in security systems that rely on smart cards. In this scenario, a user is given a code which is entered on the card - this represents the challenge. The card then displays a new code the user can provide to allow authorization - the response.